-LRB- CNN -RRB- -- Part of Robert Ferrante 's job had been to manage a laboratory that conducted clinical trials using various drugs and chemicals .

Until he was accused of using one of those substances -- cyanide -- to kill his wife .

On Friday , a Pennsylvania jury determined that this accusation was well founded , convicting the University of Pittsburgh medical researcher and professor of murder in death of 41-year-old Autumn Klein .

As juror Helen Ewing told reporters afterward , `` It was very hard for me to accept and to believe that he could have done it .

`` But I felt that the facts were clear , and I could n't argue with them . ''

For many on the outside , there seemed little amiss in the lives of Ferrante and Klein . They both had successful careers , including Klein as a top neurologist at the University of Pittsburgh Medical Center . Their house was brightened by Klein 's then-6-year-old daughter , Cianna . And they 'd just returned from a trip to Puerto Rico .

`` I 've never seen anything to suggest they were anything but a happy couple with a beautiful little girl , '' their neighbor Blithe Runsdorf said .

Then , on April 17 , 2013 , Ferrante called 911 and said his wife was `` conscious and breathing , but not alert '' inside their Pittsburgh home .

`` Please , please , please , '' he said . '' ... I think my wife is having a stroke . ''

When paramedics arrived , they found Klein on the floor of the kitchen with a plastic bag containing creatine .

She died three days later .

According to a criminal complaint , several text messages sent between the couple suggest Ferrante urged Klein to try using creatine to get help her get pregnant .

Whatever Ferrante 's rationale , there 's no scientific consensus that creatine supplements -- which some use to build muscle mass and may have medical value -- help with female fertility ; in fact , the National Institutes of Health says pregnant women should not use creatine .

Regardless , authorities say it was n't the creatine that killed Klein -- but rather cyanide that had been mixed with it .

One day before Klein fell ill , Ferrante had used a credit card to place an overnight order for more than a half-pound of cyanide . At the time the order was placed , there were no active projects at Ferrante 's lab that involved the use of cyanide , according to the complaint . And when investigators looked at the bottle , they found that over 8 grams of cyanide were missing from it .

Cyanide is often used in research laboratories for experiments . In humans , in which it interferes with a body 's ability to use oxygen to produce energy , it can be deadly .

In July 2013 , Ferrante was charged in his late wife 's death , arrested in West Virginia , then extradited back to Pennsylvania .

Accused professor waives extradition

And why did Autumn Klein die ?

More than a week after her collapse , after being told that she 'd been fatally poisoned with cyanide , Ferrante himself asked detectives , `` Why would she do that to herself ? '' A few seconds later , according to the complaint , he added : `` Who would do this to her ? ''

Another neighbor of the couple , who asked not to be identified , said it was no secret that Klein wanted another baby . But she told the neighbor 's wife Ferrante did not share that desire .

The criminal complaint raises another source of friction : Ferrante confronted his wife three times within weeks of her death about whether or not she was having an affair .

`` Further , evidence has been uncovered that reflects that the victim intended to have a conversation with Ferrante and Ferrante would ` not like the discussion , ' '' the complaint adds .

The case lingered for months , before finally going to trial in October .

Dozens of witnesses took the stand , perhaps none more key than Ferrante himself .

His lawyer , Bill Difenderfer , said after the verdict that he thought his client `` did extremely well '' on the stand . `` I thought he was very candid ... and he was telling the truth . ''

Yet , rather than be convinced of his innocence , jurors said that inconsistencies in his testimony played a significant role in their guilty verdict .

`` I think he has excellent coaches , '' Ewing said . `` I think he had a year to think about the story he wanted to tell . ''

Difenderfer said that it 's going to take time to review the `` 80-plus search warrants , multitudes of evidence -LRB- and -RRB- terabytes of information '' before deciding on the defense team 's next steps , including a possible appeal .

Klein 's parents , meanwhile , returned home to care for young Cianna and cherish the memories of the girl 's late mother .

`` While we are pleased that the person responsible for Autumn 's death has been brought to justice , '' the parents said in a statement , `` nothing will ever fill the emptiness that we feel in our family and in our hearts . ''

CNN 's Carma Hassan and Julia Lull contributed to this report .

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A Pennsylvania jury convicts Robert Ferrante of murder in his wife 's death

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Ferrante , who managed a scientific lab , bought cyanide just before she fell ill

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Authorities say the wife , Dr. Autumn Klein , was killed by cyanide poisoning

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A juror says : `` The facts were clear , and I could n't argue with them ''